1. Field of the Invention
This invention relates to a method and apparatus for storing radioactive materials or harmful substances by detaining them in a solid material.
2. Description of the Prior Art
It is strongly required nowadays to develop a technique for disposal or storing of the radioactive wastes coming from re-processing steps of nuclear fuels. Among such radioactive wastes, a typical example of gaseous material is Kr-85. Since Kr-85 has a half-life period of 10.7 years, it is necessary to store Kr-85 safely for at least 100 years. But, a gas cylinder which is widely used nowadays fails to meet the requirement of such a long period of safe storage.
Japanese Patent Disclosure No. 89799/75 proposes a method of storing radioactive materials or harmful materials into a solid material, which comprises bombarding the solid material with ionized radioactive materials such as Kr-85. This publication also teaches the idea of forming a metal layer by sputtering or vapor deposition on the surface of the solid material having the radioactive material implanted thereinto so as to prevent the implanted material from being released from the solid material. For example, implantation of ionized Kr-85 is stopped and, then, a metal layer is newly formed by sputtering on the surface of the solid material into which the ionized Kr-85 has been implanted. The newly formed metal layer serves to ensure detaining the implanted material in the solid material and, at the same time, provides a new solid material for multilayer implantation. Then, a cycle of ion implantation into the new metal layer and formation of an additional metal layer by sputtering is repeated several times.
Certainly, the method disclosed in the prior publication mentioned above permits storing radioactive wastes safely and advantageously over a long period of time, but leaves room for further improvements. Namely, the ion implantation and the metal layer formation are carried out independently, leading to troublesome operations and low processing efficiency. Particularly, the sputtering process employed for forming a metal layer on the surface of a solid material necessitates electrode replacement etc., resulting in an inefficient storing operation.